Rabbits are small mammals. The male is called a buck and the female is a doe; a young rabbit is a kitten or kit. Rabbits are herbivores that feed by grazing on grass, forbs, and leafy weeds. In consequence, their diet contains large amounts of cellulose, which is hard to digest. Rabbits re ingest their own droppings to digest their food further and extract sufficient nutrients. This double-digestion process enables rabbits to use nutrients that they may have missed during the first passage through the gut, as well as the nutrients formed by the microbial activity and thus ensures that maximum nutrition is derived from the food they eat. This process serves the same purpose within the rabbit as rumination does in cattle and sheep. Rabbits are incapable of vomiting.